Add nginx HTTP Basic Auth for production

A custom entrypoint generates /etc/nginx/.htpasswd at container startup
from AUTH_USER and AUTH_PASSWORD env vars (via openssl). No credentials
are baked into the image. Pass AUTH_USER and AUTH_PASSWORD in docker-compose.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -6,3 +6,5 @@ services:
       - "3000:80"
     environment:
       - FOOTBALL_API_KEY=${FOOTBALL_API_KEY}
+      - AUTH_USER=${AUTH_USER}
+      - AUTH_PASSWORD=${AUTH_PASSWORD}